Electron and conventional microscopy show the venom of four poisonous spiders, Loxosceles reclusa, (Gertsch and Mulaik), Latrodectus mactans, (F), Dugesiella hentzi, (Girard), and Lycosa rabida (Walkanaer) consist of paired gland sacs, ducts, and fangs. The venom glands were surrounded by spirally wound striated muscle. The glandular epithelia of "unmilked" spiders were basically columnar. The lumen of glands from unmilked spiders showed massive retention of venom in membrane limited packets. Tarantual - Major constituents of tarantula venom, D. hentzi, are hyaluronidase, a necroxic toxin and nucleotides. The toxin has been purified and characterized chemically and biologically. Brown spider, L. recluse venom extracts have been prepared which produce lesions and death in test animals. These toxins have been identified and partially characterized. A comparative study of venoms from 4 species of scorpions, Scorpionida has been completed as well as a detailed study of enzymes and toxins from Palamneus gravimanus. The major constituents include hyaluronidase, alkaline phosphatase, and two or more protein toxins. Rabbit antisera have been prepared which protect mice from the venom toxins of tarantula or brown spider.